1. Field of the Invention
This invention relates to a negative planographic printing plate precursor for direct image writing with an infrared laser, capable of high speed processing, and in particular, when stacked, to a planographic printing plate precursor with improved adhesion resistance of a surface on the light sensitive layer side of the planographic printing plate precursor to a surface on a support body side of the planographic printing plate precursor.
2. Description of the Related Art
Conventionally PS plates, of a lipophilic light sensitive resin layer provided on a hydrophilic support body, are widely used for planographic printing plate precursors. The plate-making method thereof is normally after mask exposure through a lith film (surface light exposure), obtaining a desired printing plate by dissolving away the non-image areas. Recently, digitalized electronic processing, storing and output of image data using a computer has become common. New image output systems, which are applicable to such digitalized technologies, have variously become useable in practice. As a result of this it has become desirable to directly manufacturing printing plates—computer to plate (CTP)—by scanning according to digitalized image information with light that is highly directionable, like lasers, and not through lith films. Obtaining planographic printing plate precursors which are applicable to such a process has become an important technological challenge.
As such planographic printing plate precursors which can undergo scanning exposure, structures that have a lithophilic photosensitive resin layer (referred to below as a photosentivive layer), which contains a light sensitive compound that can generate active species such as radicals and Bronsted acids when exposed with laser light, on a hydrophilic support body are already on the market.
These planographic printing plate precursors are scanned with a laser according to digital information to generate active species, and by this action the photosensitive layer is rendered insoluble by either physical change or chemical change. Following on from this, by developing processing a negative planographic printing plate can be obtained. In particular, planographic printing plates provided with a hydrophilic support body on which is provided a photo polymerizing type light sensitive layer, including a photopolymerization agent which is superior in photosensitive speed, an addition polymerizable unsaturated ethylene compound, and, as required, an oxidation exclusion protecting layer, are both superior in manufacturability, and further more easy to develop process, have the benefit of good definition and ink adherence, and hence printing plates with desirable printing characteristics can be obtained.
Conventionally, in order to promote the curing reaction of the photosensitive layer, there is a method of providing over the photosensitive layer a protecting layer containing a water soluble polymer, and a method of providing an inorganic material lamellar compound and a protecting layer containing water soluble polymer are known (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-38633). However, in a light polymerizing planographic printing plate precursor of such a structure, while by the presence of the protecting layer the curing reaction of the photosensitive layer can be promoted, the sensitivity is not sufficient, and there is a challenge to make it highly sensitive.
Also, regarding the productivity of plate making of the ease of developing processing light polymerizing planographic printing plate precursors, it is becoming important to reduce the time required for the exposure process. In the exposure process, normally, the precursor plates are provided in stacks, with interleaving papers inserted between precursor plate and precursor plate, having the function of preventing adhesion between the precursor plates themselves. Because of this, the inefficiency of having to remove the interleaving papers in the exposing process has become a problem. In order to make the exposing process efficient, it is desirable to improve the adhesion resistance between planographic printing plate precursors themselves, and, by using stacks without interleaving papers interleaved between the precursor plates, be able to eliminate the interleaving paper removal process.